The present invention relates to a database system and a method for accessing a center server and a database and more particularly, to a database system for replicating databases in a single or a plurality of storage subsystems which are connected to a network and located remotely and permitting replicated databases to be accessed in a consolidated fashion and a method for accessing a center server and databases in that system.
As a conventional technique concerning a method for replicating a remotely located database, a technique of database replication has been known in which data is replicated between servers mutually connected through a LAN or WAN. As another conventional technique, a technique of database hub has been known according to which inquiries are made to distributed database management systems during execution of the inquires and results returned from the individual database management systems are consolidated so as to be exhibited as one result. Further, known as still another conventional technique directed to preparation of a replication of a database at a remote location is a technique of disaster recovery using a volume replication function owned by a storage device.
Known as a prior art concerning the database hub is a technique described in “Data Joiner”, International Business Machines Corporation, Internet document searched on Nov. 11, 2002, located at the website www-3.ibm.com/software/data/datajoiner and known as prior arts concerning the disaster recovery are techniques described in “Building Storage Networks” by Marc Farley, second edition. Osbone/McGraw-Hill Corp., 2001, pp. 118–124 and described in “HiRDB version 6”, Hitachi Com. Software Department, Internet document searched on Nov. 11, 2002, located at the website www.hitachi.co.jp/Prod/comp/soft/opene/hirdb/v6/outline/confv6.
When a method based on the aforementioned database replication is used as means for getting a consolidated access to a plurality of databases at remote locations, the LAN or WAN is used for transfer of data, raising a problem that much time is consumed for replication of data. In a method using the database hub, the remotely located database management systems are accessed during execution of inquiries, with the result that the response time is degraded and besides, when a large number of results are brought about, a large amount of data must be transferred through the medium of the LAN or WAN, giving rise to a problem that the search performance is degraded. In addition, the method of disaster recovery using the volume replication function the storage unit has is back-up for a database on the replication side to recover and disadvantageously, it cannot afford to consolidate a plurality of databases.